Materials Science

Extra-Strong Sleeves

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Science  14 Dec 2007:
Vol. 318, Issue 5857, pp. 1697
DOI: 10.1126/science.318.5857.1697b

The sponge-like structure of metallic foams (up to 80% void fraction) has fostered applications in impact-absorbing materials, acoustic insulation, and lightweight structural materials. More recent attention has focused on periodic cellular materials (PCMs), wherein the remaining mass exclusively forms load-bearing trusses that are loaded in tension or compression rather than bending. A second design strategy for strengthening metals is to reduce grain size to the nanometer scale and thereby localize a larger number of atoms at grain boundaries, reducing their mobility. Suralvo et al. created a PCM by stretching a square punched aluminum sheet to displace half the nodes above and the other half below the initial starting plane. They then electroplated a nanocrystalline alloy of nickel and iron to form a sleeve around the struts and nodes of the trusses, with the thickness controlled over a 75- to 400- μm range by the deposition time. The loading stiffness more than doubled and the peak strength increased 10-fold. The specific strength, which accounts for changes in density, also increased almost threefold. — MSL

Scripta Mater. 58, 247 (2008).

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